This invention concerns water and wastewater treatment systems and methods, and specifically relates to sludge thickening processes in a treatment system, wherein sludge settles to the bottom of a tank, and to improvements in the thickener and process.
Thickened sludge, particularly sludge at water treatment plants, often tends to entrap the rake arms of the thickener in “mud”, tripping alarms and incapacitating the sludge thickener mechanism by stopping the rake arms when the drive mechanism becomes overloaded. Also, when the thickened sludge is withdrawn from the thickener, it tends to “post hole” at the withdrawal point, where the solids concentration withdrawn begins at a high level and then over a short period of time thins out for the duration of the withdrawal period, or wherein the thickener intermittently delivers high concentrated solids and low concentrated solids as the rake arm passes over the withdrawal point.
This strong fluctuation in the level of solids concentration in the output of a thickener makes operation of a downstream dewatering device difficult, especially when a dewatering floc aid such as polymer is used in a constant amount, or when the dewatering device requires a relatively constant feed solids concentration because of the operation of screw presses, belt presses or centrifuges.